1. Field of the Invention
The present invention relates to valve body and condensate holding tank systems and methods for use in delayed coker unit operations. In particular, the present invention relates to allowing accumulated condensate and particulate matter in a valve body or in a condensate holding tank to be flushed into a coker pit by water or other solvent.
2. Background
Petroleum refining operations in which crude oil is processed frequently produce residual oils. Many oil refineries recover valuable products from the heavy residual hydrocarbons. Residual oil, when processed in a delayed coker is heated in a furnace to a temperature sufficient to cause destructive distillation in which a substantial portion of the residual oil is converted, or “cracked” to usable hydrocarbon products and the remainder yields petroleum coke, a material composed mostly of carbon.
Generally, the delayed coking process involves heating the heavy hydrocarbon feed from a fractionation unit, then pumping the heated heavy feed into a large steel vessel commonly known as a coke drum. The unvaporized portion of the heated heavy feed settles out in the coke drum, where the combined effect of retention time and temperature causes the formation of coke. Vapors from the top of the coke vessel are returned to the base of the fractionation unit for further processing into desired light hydrocarbon products. Normal operating pressures in coke drums typically range from twenty-five to fifty p.s.i, and the feed input temperature may vary between 800° F. and 1000° F.
The structural size and shape of the coke drum varies considerably from one installation to another. Coke drums are generally large, upright, cylindrical, metal vessel ninety to one-hundred feet in height, and twenty to thirty feet in diameter. Coke drums have a top head and a bottom portion fitted with a bottom head. Coke drums are usually present in pairs so that they can be operated alternately. Coke settles out and accumulates in a vessel until it is filled, at which time the heated feed is switched to the alternate empty coke drum. While one coke drum is being filled with heated residual oil, the other vessel is being cooled and purged of coke.
Coke removal, also known as decoking, begins with a quench step in which steam and then water are introduced into the coke filled vessel to complete the recovery of volatile, light hydrocarbons and to cool the mass of coke. After a coke drum has been filled, stripped and then quenched so that the coke is in a solid state and the temperature is reduced to a reasonable level, quench water is drained from the drum through piping to allow for safe unheading of the drum. The drum is then vented to atmospheric pressure when the bottom opening is unheaded, to permit removing coke. Once the unheading is complete, the coke in the drum is cut out of the drum by high pressure water jets.
During the unheading and decoking process, the bottom deheader unit is often pressurized by steam and exposed to liquid and solid particular matter falling from the coke drum. Accordingly, the art of decoking a coke drum may be improved by developing a bottom deheading unit which has the ability to drain excess condensate from steam and to be flushed of any solid particulate matter which accumulates.